45 Strafe/ja

45° Strafeとは、通常よりも高い速度を得られる技術である。

strafeキーを入力し、45°方向に振り向くことで実行できる（名前の由来はそこから）。

45° Strafeは以下のどちらでも可能:

• 左45°に振り向き、右Strafeキーを入力。
• 右45°に振り向き、左Strafeキーを入力。

振り向きは素早く（1tick以内）かつ正確（誤差最大±11.5°、±0°に近いほど良い）でなければならないため、安定して実行するのは難しい。

1bm 4.375bなど、45° strafeが必須のジャンプも存在する。

動きへの影響

毎tick、プレイヤーはキー入力などの要素に基づいた加速度を得る。

• When moving forward (without strafing), the acceleration gained is scaled by $0.98$

• When strafing, the acceleration is scaled by $1.0$

Therefore, 45° Strafe is ${1.0 \over 0.98}$ times faster than regular movement (about 2% faster).

Special case: 45° Sneak

• When sneaking forward (without strafing), the acceleration gained is scaled by $0.98$
• When strafing while sneaking, the acceleration gained is scaled by $0.98{\sqrt {2}}$ (≈ 1.386)

45° Sneak is used for no momentum jumps (example).

Outside of parkour, it's notably used for bridging, as it's ~41% faster than regular sneaking.

解説

Below is a simplified version of the horizontal movement source code.

/* 
 * Code from Entity and EntityLivingBase
 * Unnecessary or unrelated code is stripped out
 */
</div>

<div lang="en" dir="ltr" class="mw-content-ltr">
public void onLivingUpdate()
{
    /* 
     * moveStrafing and moveForward represent relative movement.
     * moveStrafing = 1.0 if moving left, -1.0 if moving right, else 0.0
     * moveForward = 1.0 if moving forward, -1.0 if moving backward, else 0.0
     *
     * Furthermore, moveStrafing and moveForward *= 0.3 if the player is sneaking.
     */
</div>

    <div lang="en" dir="ltr" class="mw-content-ltr">
this.moveStrafing *= 0.98F;
    this.moveForward *= 0.98F;
    this.moveEntityWithHeading(this.moveStrafing, this.moveForward);
}
</div>



<div lang="en" dir="ltr" class="mw-content-ltr">
public void moveEntityWithHeading(float strafe, float forward)
{
    /* inertia determines how much speed is conserved onto the next tick */
    float mult = 0.91F;
    if (this.onGround)
    {
        /* Get slipperiness 1 block below the player */
        mult *= getBlockSlipperinessAt(this.posX, this.getEntityBoundingBox().minY - 1, this.posZ);
    }
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    <div lang="en" dir="ltr" class="mw-content-ltr">
/* acceleration = (0.6*0.91)^3 / (slipperiness*0.91)^3) */
    float acceleration = 0.16277136F / (mult * mult * mult);
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    <div lang="en" dir="ltr" class="mw-content-ltr">
float movementFactor;
    if (this.onGround)
        movementFactor = this.landMovementFactor * acceleration;
        /* base: 0.1; x1.3 if sprinting, affected by potion effects. */
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    <div lang="en" dir="ltr" class="mw-content-ltr">
else
        movementFactor = this.airMovementFactor; 
        /* base: 0.02; x1.3 if sprinting */
</div>

    <div lang="en" dir="ltr" class="mw-content-ltr">
this.updateMotionXZ(strafe, forward, movementFactor); 
    this.moveEntity(this.motionX, this.motionY, this.motionZ);
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    <div lang="en" dir="ltr" class="mw-content-ltr">
this.motionY -= 0.08D; /* gravity */
    this.motionY *= 0.98D; /* drag */
</div>

    <div lang="en" dir="ltr" class="mw-content-ltr">
this.motionX *= mult;
    this.motionZ *= mult;
}
</div>



<div lang="en" dir="ltr" class="mw-content-ltr">
public void updateMotionXZ(float strafe, float forward, float movementFactor)
{
    /*
     * This function is responsible for the existence of 45° strafe. The geometry doesn't seem to make sense...
     * Note that:
     *     - Sprint multiplier is contained within "movementFactor"
     *     - Sneak multiplier is contained within "strafe" and "forward"
     * This is likely because Sneaking was implemented long before Sprinting
     */
    float distance = strafe * strafe + forward * forward;
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    <div lang="en" dir="ltr" class="mw-content-ltr">
if (distance >= 1.0E-4F)
    {
        distance = MathHelper.sqrt_float(distance);
            
        if (distance < 1.0F)
            distance = 1.0F;
</div>

        <div lang="en" dir="ltr" class="mw-content-ltr">
distance = movementFactor / distance;
        strafe = strafe * distance;
        forward = forward * distance;
        float sinYaw = MathHelper.sin(this.rotationYaw * Math.PI / 180.0F);
        float cosYaw = MathHelper.cos(this.rotationYaw * Math.PI / 180.0F);
        this.motionX += strafe * cosYaw - forward * sinYaw;
        this.motionZ += forward * cosYaw + strafe * sinYaw;
    }
}